941. Valid Mountain Array

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941. Valid Mountain Array

Description

Given an array of integers arr, return true if and only if it is a valid mountain array.

Recall that arr is a mountain array if and only if:

  • arr.length >= 3

  • There exists some i with 0 < i < arr.length - 1 such that:

  • arr[0] < arr[1] < ... < arr[i - 1] < arr[i]

  • arr[i] > arr[i + 1] > ... > arr[arr.length - 1]

Example 1:

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Input: arr = [2,1]
Output: false

Example 2:

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Input: arr = [3,5,5]
Output: false

Example 3:

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Input: arr = [0,3,2,1]
Output: true

Constraints:

  • 1 <= arr.length <= 10^4
  • 0 <= arr[i] <= 10^4

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    bool validMountainArray(vector<int>& arr) {
        int n = arr.size();
        if (n < 3) {
            return false;
        }
        int i = 0;
        while (i < n - 1 && arr[i] < arr[i + 1]) {
            i++;
        }
        if (i == 0 || i == n - 1) {
            return false;
        }
        while (i < n - 1 && arr[i] > arr[i + 1]) {
            i++;
        }
        return i == n - 1;
    }
};